make variable-reference->namespace enable top-level mode

The namespace returned by `variable-reference->namespace` (or
`namespace-anchor->namespace`) may be used via `eval` to define new
bindings, so enable top-level binding support for the namespace.

pkgs/racket-test-core/tests/racket/module.rktl

@@ -1780,6 +1780,21 @@ case of module-leve bindings; it doesn't cover local bindings.
 
 (test 5 dynamic-require ''module-that-exports-phase-2-x-at-phase-0 'x)
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Check that
+;; `namespace-anchor->namespace` internally enables top-level mode for
+;; binding handling:
+
+;; Example from Alex Knauth:
+(module module-that-uses-eval-to-define-a-macro-in-its-own-namespace racket/base
+  (require (for-syntax racket/base))
+  (define-namespace-anchor a)
+  (define ns (namespace-anchor->namespace a))
+  (eval '(define-syntax x (λ (stx) #'333)) ns)
+  (define result (eval 'x ns))
+  (provide result))
+
+(test 333 dynamic-require ''module-that-uses-eval-to-define-a-macro-in-its-own-namespace 'result)
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)

racket/src/racket/src/env.c

@@ -2120,6 +2120,7 @@ static Scheme_Object *do_variable_namespace(const char *who, int tl, int argc, S
     /* return env directly; need to set up  */
     if (!env->phase && env->module)
       scheme_prep_namespace_rename(env);
+    env->interactive_bindings = 1;
   } else {
     /* new namespace: */
     Scheme_Env *new_env;